The invention relates generally to a circuit breaker. More particularly the present invention relates to a high-voltage circuit breaker, insulated by SF.sub.6 gas and including an arrangement for directing a blast of SF.sub.6 gas on to the arc.
The circuit breaker further includes a fixed contact part and a movable switching piece which is provided with a blast nozzle and may be actuated by a drive. A compression space is rendered smaller during the process of tripping out, such that a flow of gas moves toward the blast nozzle and the arc produced. The compression space includes a movable piston in a cylinder which piston is pulled toward a stationary cylinder-bottom. Alternatively, a movable cylinder may be pulled over a stationary piston head, in order to generate the gas flow during the process of tripping out.
Circuit breakers of the above-mentioned type are known. In circuit breakers of this type, in order to direct a blast of gas onto the arc, the movable piston or the movable cylinder is, in each case, pulled towards the stationary part. In this way, the size of the compression space is reduced and the gas is compressed to a specified pressure which is sufficient to blast the gas on to the arc.
In these known blast-piston breakers, the energy for compressing the extinguishing gas in the compression space is provided solely by the drive of the circuit breaker. The dimensions of this drive must therefore be chosen so as to ensure that it is sufficiently powerful.
It is known, for example, in U.S. Pat. No. 3,331,935, to insert an auxiliary piston into the compression space in order to increase the compression in this space whenever the circuit breaker trips out. This auxiliary piston is driven by the force of a spring. The mechanism for actuating and driving the auxiliary piston is a latch-type mechanism and consequently is comparatively complicated. Accordingly, it is extremely difficult on account of this type of construction to reduce the overall size of the circuit-breaker drive.
Accordingly, an object of the present invention is to provide a circuit breaker of the type initially mentioned, which is of simpler construction, and which, as a consequence of this simpler construction, possesses a higher efficiency, accompanied by a smaller drive. This object and others are achieved according to the present invention.
Electrodynamic drives are known (compare Swiss Patent No. 594,977) but these drives are not used to actuate an auxiliary piston. These drives operate, in the event of a short-circuit, to additionally accelerate either the complete movable system of the circuit breaker, or at least the movable system of the extinguishing chamber. Also, these drives may be used to at least maintain the tripping-out speed at a value corresponding to the speed of the system when not under load.
The solution according to the present invention provides a circuit breaker in which the compression energy is produced in accordance with the following basic principle:
In a range corresponding to the rated currents and to small short-circuit currents, the compression energy is produced essentially by the circuit breaker drive. The circuit breaker drive is utilized up to current values corresponding to approximately 30% of the short-circuit current at which the circuit breaker is rated to trip out. Since, in this current range, the gas pressure in the compression volume of the breaker required for extinguishing the current is low, the breaker drive can be designed with a correspondingly low basic speed. Consequently, the drive can be dimensioned in a manner consistent with an advantageous low cost. PA1 In a range corresponding to comparatively high short-circuit currents up to the short-circuit current at which the circuit breaker is rated to trip out, the pressure to which the extinguishing gas must be compressed in order to extinguish the arc is produced by the auxiliary piston. The auxiliary piston is driven by magnetic energy of the short-circuit current.
In a further aspect according to the present invention, a coil is provided as the means for generating the magnetic field. The coil concentrically surrounds the compression space. At the same time, a cylindrical inner shell is preferably provided inside a cylindrical outer shell which bounds the compression space externally. The inner shell is arranged with a clearance relative to the outer shell and insulated therefrom with the coil being located between the outer and inner cylindrical shells.